1. Field of the Invention
This invention relates generally to a puller to extract the tube bundles from a heat exchanger and more particularly to a puller which can be suspended from a crane to work on elevated heat exchangers.
2. Prior Art
Shell and tube heat exchangers constitute a substantial portion of heat transfer equipment in chemical process plants. Heat transfer between two streams at different temperatures is accomplished by flowing one stream through tubes arranged in a tube bundle and flowing the second stream past the outside of the tubes, on the shell side. Scale and sediment build up on both the outside and inside of the tubes during use. After a period, these deposits decrease the efficiency of heat transfer across the tube walls. The heat exchanger is cleaned by extracting the tube bundle from the shell and hydro-blasting the inside of the shell and the inside and outside of the tubes. Examples of the cleaning process may be found in Simon, U.S. Pat. No. 4,323,398 and Cradeur, U.S. Pat. No. 3,938,535.
Occasionally, the heat exchangers are located high above the ground in the superstructure of a process unit. Several prior art tube bundle pullers are adapted to be lifted by a crane to service these elevated exchangers such as Travis, U.S. Pat. Nos. 3,567,044 and 3,836,015, Postlewaite, U.S. Pat. No. 3,180,498 and Coffey, U.S. Pat. No. 4,227,854.
Pulling the tube bundle of a heat exchanger requires a significant force. The tube bundle itself typically weighs 15-20,000 lbs. and it is not unusual for there to be an additional force required to break the bundle loose from where it has adhered to the shell. In the above mentioned bundle pullers a variety of mechanisms have been used to apply the necessary force, such as hydraulic cylinders and air motor/screw combinations. In the above bundle pullers, the source of either the hydraulic power or compressed air is an auxillary unit not contained on the bundle puller. The auxillary unit presents an additional line which must be connected to the bundle puller. Not only does this decrease the mobility of the bundle puller, but significant power losses can occur due to pressure drops along lengths of hose.
Tube bundles as long as 20 feet are not uncommon. The tubes are usually secured at one end in a tube sheet and may be U shaped or straight. If straight, the tubes are usually secured at their opposite end to a second tube sheet. Along the length of the tubes, baffles are provided to both hold the tubes together and to direct the flow of fluid on the shell side of the exchanger. Once the tube bundle is removed from the shell, means must be provided to support the bundle. Prior art methods of supporting the tube bundle upon removal are slings as shown in Murphy, U.S. Pat. Nos. 3,658,191 and 3,765,544 and support trolleys as shown in Coffey, U.S. Pat. No. 4,227,854.